As a work machine, there has been known a hybrid construction machine in which an engine drives a generator motor and a hydraulic pump, whereby an electric motor for an upper rotary body where a cab and the like are provided is driven by electric power generated by the generator motor while a hydraulic actuator for an operating device and a hydraulic motor for a traveling device are driven by a pressure oil from the hydraulic pump. The electric power generated by the generator motor is charged in a capacitor serving as an electric storage device and is outputted from the capacitor to the electric motor through an inverter.
In such a hybrid construction machine, on performing various maintenance, for security reasons, a voltage of the capacitor needs to be reduced to a predetermined level and a contactor provided at an output portion from the capacitor needs to be turned off (open). Thus, careful attention needs to be paid to avoid output of the electric power charged in the capacitor.
Accordingly, an inspection window for checking a discharge amount of the capacitor and conditions of the contactor is provided on an outer surface of a casing of the capacitor. By visually checking a lighting condition of an LED (light emitting diode) through the inspection window, the conditions of the contactor and a charging condition of the capacitor can be recognized. As such an inspection window, an inspection window (transparent window) provided on an upper case of a power supply package has been typically known although the inspection window is not used for a hybrid construction machine (see Patent Literature 1).
Patent Literature 1 discloses that the inspection window is provided for checking a battery fluid level indicator housed inside the case and for checking various conditions of the battery using a battery hydrometer and the like.